Chapter 4 Ap Statistics

Voluntary Response Sample

A sample in which people decide whether to join the sample in response to an open invitation. Shows bias

Basic Data Ethics

All planned studies must be reviewed in advance by an institutional review board charged with protecting the safety and well-being of the subjects. All individuals who are subjects in a study must give their informed consent before data are collected. All individual data must be kept confidential. Only statistical summaries for groups of subjects may be made public.

Principles of Experimental Design

Control for lurking variables that might affect the response: Use a comparative design and ensure that the only systematic difference between the groups is the treatment administered. Random assignment: Use impersonal chance to assign experimental units to treatments. This helps create roughly equivalent groups of experimental units by balancing the effects of lurking variables that aren't controlled on the treatment groups. Replication: Use enough experimental units in each group so that any differences in the effects of the treatments can be distinguished from chance differences between the groups.

Inference

The process of drawing conclusions about a population on the basis of sample data

Placebo

a "dummy pill" or inactive treatment that is indistinguishable from the real treatment

Block

a group of experimental units that are known before the experiment to be similar in some way that is expected to affect the response to the treatments

Control Group

a group that receives an inactive treatment or an existing baseline treatment

Table of Random Digits

a long string of the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 with these properties: • Each entry in the table is equally likely to be any of the 10 digits 0 - 9. • The entries are independent of each other. That is, knowledge of one part of the table gives no information about any other part.

Matched-Pairs Design

a randomized blocked experiment in which each block consists of a matching pair of similar experimental units

Treatment

a specific condition applied to the individuals in an experiment

Sample Survey

a study that uses an organized plan to choose a sample that represents some specific population

Level

a treatment formed by combining a specific value

Lurking Variable

a variable that is not among the explanatory or response variables in a study but that may influence the response variable

Statistically Significant

an observed effect so large that it would rarely occur by chance

Significant

an observed effect that is too large to have occurred by chance alone

Convenience Sample

choosing individuals who are easiest to reach results

Stratified Random Sample

classify the population into groups of similar individuals, called strata. Then choose a separate SRS in each stratum and combine these SRSs to form the full sample.

Simple Random Sample (SRS)

consists of n individuals from the population chosen in such a way that every set of n individuals has an equal chance to be the sample actually selected

Experiment

deliberately imposes some treatment on individuals to measure their responses

Cluster Sample

divide the population into smaller groups. Ideally, these clusters should mirror the characteristics of the population. Then choose an SRS of the clusters. All individuals in the chosen clusters are included in the sample

Random Assignment

experimental units are assigned to treatments at random, that is, using some sort of chance process

Factors

explanatory variables in an experiment

Strata

groups of similar individuals

Causation

in its simplest form...the relationship between cause and effect

Lack of Realism

limit our ability to apply the conclusions of an experiment to the settings of greatest interest

Wording of Questions

most important influence on the answers given to a sample survey. Creates strong bias

Double-Blind Experiment

neither the subjects nor those who interact with them and measure the response variable know which treatment a subject received

Observational Study

observes individuals and measures variables of interest but does not attempt to influence the responses

Non-response

occurs when an individual chosen for the sample can't be contacted or refuses to participate

Undercoverage

occurs when some groups in the population are left out of the process of choosing the sample

Confounding

occurs when two variables are associated in such a way that their effects on a response variable cannot be distinguished from each other

Margin of Error

results from a random sample that sets bounds on the size of the likely error

Well-Designed Experiment

tells us that changes in the explanatory variable cause changes in the response variable

Bias

the design of a study that systematically favors certain outcomes

Population

the entire group of individuals about which we want information

Sample

the part of the population from which we actually collect information

Replication

the practice of using enough subjects in an experiment to reduce chance variation

Randomized Block Design

the random assignment of experimental units to treatments is carried out separately within each block

Experimental Units

the smallest collection of individuals to which treatments are applied

Completely Randomized Design

the treatments are assigned to all the experimental units completely by chance

Subjects

when the units are human beings